1. Field of the Invention
This invention relates to the chemical analysis of substances, and more particularly relates to apparatus for the automatic analysis of biological fluids. Even more specifically, this invention relates to medical testing devices particularly adapted for veterinary testing purposes wherein a change in an optical characteristic of a sample is sensed and analyzed automatically by the device.
Increasingly, the population has relied upon competent medical assistance to solve individual medical problems to a greater and greater extent. This factor, coupled with the ever growing wealth of medical knowledge, has resulted in a vast upsurge in the number of tests of various types performed as part of the diagnosis or health monitoring process. As a result, there is an increasing need for apparatus for performing such tests in an inexpensive fashion, which apparatus can be operated by relatively unskilled personnel and which will eliminate most opportunities for unreliability of results due to human error.
2. Description of the Prior Art
In recent years, a number of automated systems have been developed for carrying out quantitative chemical analysis of fluid samples. Many of the commercially available systems utilize liquid reagents and require analyzer equipment having intricate solution handling and transport capabilities. Such equipment can be referred to as "wet chemistry" analyzers. For example, U.S. Pat. No. 3,788,816, which issued to D. G. Rohrbaugh et al., discloses a liquid analysis system in which a turntable carries a plurality of receptacles containing samples to be analyzed and a plurality of tube modules which are adapted to receive preset volumes of sample and reagent. Coaxially disposed relative to the turntable is a vertically movable rotary element comprising a probe tip which serves to dispense reagents and to transfer sample to a spectrophotometer.
Wet chemistry analyzers, such as described above, are usually complex and expensive, require skilled operators and necessitate a considerable expenditure of time and effort in repetitive cleaning operations.
As an alternative to liquid analysis systems, various analyzers have been developed for automated test procedures involving essentially dry, analytical elements, which elements offer substantial storage and handling conveniences when compared to "wet chemistry" instruments.
The "dry" analytical elements are preferably in the form of test slides. The test slides are formed as a multi-layer element containing the necessary reagents for reaction with components of a biological fluid, such as blood serum, deposited thereon. Certain reactions colorimetrically produce a change in optical density which is sensed by a reflectometer or other device, the amount of light reflected from the element varying in accordance with the reaction and being indicative of the amount of a particular component present in the fluid.
In a typical chemical analyzer, such as described in U.S. Pat. No. 4,296,070, which issued to Michael S. Montalto et al., the slides, which are essentially planar and contain reagents in dry form, are loaded into a cartridge and fed from the cartridge into a metering station where a predetermined amount of sample fluid is deposited on the analysis slide.
After an appropriate incubation period, the slide is moved to an analysis station where a change in the slide is sensed, the amount of change being proportional to a particular analyte in the sample fluid. The slide is used only once and is discarded after the reading is taken.